The prior art is replete with numerous examples of friction stir welding devices which are useful in welding various materials. As a general matter, friction stir welding is a technique whereby a rotating tool is brought into forcible contact with an adjacent work piece to be welded and the rotation of the tool creates frictional heating of the adjacent work piece and extensive deformation as mixing occurs along a plastic zone. Upon cooling of the plastic zone, the work pieces are joined along a welding joint. Examples of prior art friction stir welding devices and other methodology are more fully disclosed in U.S. Pat. Nos. 4,636,124; 5,460,317; 5,769,306; 5,971,247; 6,079,609; 6,173,880; 6,230,957; 6,237,835; 6,259,052; 6,484,924; 6,613,447; and 6,619,534, the teachings of which are incorporated by reference herein.
While the prior art devices, and other methodology described above have operated with some degree of success on some materials, there has been identifiable shortcomings which have detracted from the utilization of this same welding technique for welding certain harder materials. For example, for higher strength materials, such as steel, titanium, and the like, suitable friction stir welding tools have been difficult to develop due at least in part to the temperatures, and the loads that the tool receives during the friction stir welding process. In this regard, and for currently available friction stir welding tools, it is well known that these tools have a limited life cycle. Still further, these same tools are often fabricated from relatively expensive materials. Consequently, such tools are quite costly. Currently, the lifespan of such friction stir welding tools is often measured in terms of feet or tens of feet of welding per tool.
In view of this shortcoming, the friction stir welding of high strength materials such as titanium, and steel, has largely been confined to highly specialized applications where cost is largely not an issue and the number of feet of material to be welded is typically quite limited.
Therefore a friction stir welding tool which avoids the shortcomings associated with the prior art practices and methodology is the subject matter of the present invention.